I spent a lot of time modding Grados, and contrary to what Grado modders say, you can't mod a Prestige series Grado to make it into an RS1/MS-Pro -- unless you do a driver replacement like the Magnums.

Exactly!  I've said the same countless times to deaf ears over there.  I do think the SR225 is more closely related to the RS1 though. I noticed a rather obvious difference between the SR60/80 line compared to the 225/RS1 that I don't think is explained by just a dab of dynamat on the back.